Sea urchins, or urchins, are small animals with round and spiny ‘tests’ (shells) that inhabit most of the oceans in the world. The name urchin used to be a name for ‘hedgehog’ and since sea urchins inhabit the sea, they are known as the ‘sea urchins’. They belong to the phylum Echinodermata which means ‘spiny skin’ in Greek.
The Red Slate Pencil Urchin is mainly found in the tropical waters of the Indo-Pacific region, specifically in Hawaii. This type of urchin has blunt, solid spines that resemble pencils, hence the name ‘pencil urchin’. The name of the urchin also originated from the fact that its spines were once used as writing material on slate boards.
Scientific Classification
Level
Classification
Kingdom
Animalia
Phylum
Echinodermata
Class
Echinoidea
Order
Echinoida
Family
Echinometridae
Genus
Heterocentrotus
Species
H. mammillatus
Habitat
Geographical location
The Red Pencil Slate Urchin mainly resides in the Eastern Indo-Pacific Ocean that surrounds many volcanic islands including Hawaii. red pencil slate urchins are commonly found in the Hawaiian Islands (refer to figure 1). Hawaii has a very stable climate, although it may vary a bit, the temperatures are mostly the same throughout the year during winter and summer. The average temperature is 26.6°C while the ocean water temperature varies from a warm 22.7°C to 26.6°C. According to previous experiments and studies, when temperatures are higher than 21°C reproduction decreased which means that there is a slight possibility that there may be a future decrease in reproduction of the red pencil slate urchins.
Red pencil slate urchins share the same home in the Hawaiian ocean with the green sea turtle and the bottlenose dolphin, however both of these animals are not their predators.
Sunlight, storms and the effects of these aspects
Hawaii, being the absolute surfer’s paradise and number 1 holiday location, is known for its always sunny skies. On sunny days, the sun can be very intense which is not a good sign for Red Pencil Slate Urchins as, like other sea urchins; they are very sensitive to light. This explains why they normally like to hide in shallow tide pools as the coral reefs and rocks can not only let them hide from predators but also let them find shelter from the sun. Red Pencil Slate Urchins are nocturnal; they spend most of the day time hiding in between or behind rocks avoiding the sunlight (refer to figure 2) and dislodging itself to find food when night arrives.
In the past, tropical storms and hurricanes have also been responsible for wiping out a great amount of sea urchins. Living in Hawaii, an island that sits on the edge of a tropical zone, it is rather prone to occasional tropical storms which, as a result, cause large waves that can dislodge Red Pencil Slate Urchins. This can cause a decrease to their population as they can be washed away from their food source. Although hurricanes are rare in Hawaii, when it does occur it can achieve the same result, causing damage to the Red Pencil Slate Urchin population.
Food source and predators
Red Slate Pencil Urchins are herbivores; they mainly feed on kelp, seaweed and algae. They are known to be extremely abundant and can cause disturbance to the kelp-forest ecosystem. This is because they feed on the hold fasts of kelps (refer to figure 3) which causes it to detach from its anchor, disabling it from regrowth. This is where the predators of Red Slate Pencil Urchins save the kelp-forest ecosystem by feeding on sea urchins, maintaining the ecological balance and sustaining the luxuriance of kelp forests. Apart from sea grass, Red Slate Pencil Urchins also feed on dead fish, mussels and barnacles which explain how they find food at ease the coral reefs of Hawaii. However Red Slate Pencil Urchins attract many predators on the coral reefs as well and these daring predators include molluscs and fish like the spotted oceanic triggerfish which are also found mostly in coral reefs. The spotted oceanic triggerfish are exactly opposite to the Red Slate Pencil Urchins; they are active during the day while they sleep soundly in between rocks at night. They are able to feed on many sea urchins (including the Red Slate Pencil Urchin) despite their sharp spines, by flipping them over and going through the shell through the soft tissue surrounding the mouth of the sea urchin. Triggerfish are capable of flipping the sea urchin by shooting a strong jet of water while the sea urchin is relaxed (since it would be resting during day time when triggerfish are active).
[Figure 3: Video of sea urchin feeding on kelp]
Adaptations
Behavioural Adaptation #1:
Red pencil slate urchins like to use their blunt spines to fit themselves tightly into small cracks between rocks (refer to figure 4). Many tourists who go out to explore the coral reefs in Hawaii do comment on the red pencil slate urchins to “disappear and be completely out of sight during the day time and magically reappear in groups during the night”.
By doing this, the rocks offer them a very good camouflage from predators during the day time while they are resting as well as the intense sunlight that they are sensitive to. Another reason why red pencil slate urchins hide themselves in tight crevices is to prevent themselves from being washed away by big waves or currents.
Environmental pressure that might have resulted in this adaptation could be tourism. This is because many tourists who visit Hawaii like to explore the beautiful underwater world and this may cause disturbance to red pencil slate urchins, causing them to hide themselves from these unwanted visitors during day time. Also, occasional tropical storms in Hawaii may have resulted in the red pencil slate urchins “knowing” how to hide in crevices to prevent being washed away by the big waves of the aftermath.
Behavioural Adaptation #2:
Red pencil slate urchins, like other sea urchin species, are nocturnal. As previously mentioned, red pencil slate urchins spent most of their day resting in safe shelters between rocks and come out during the night to hunt. To be specific, when it is dawn, red pencil slate urchins search for a good shelter in shady crevices. During the day, they stay in their shelter and do not conduct much activity. At dusk, after 3PM, red pencil slate urchins will dislodge themselves from their shelters and start to find food. At night time, during midnight until 3AM, is the period when they’re at their most active state. Usually at this time, they would be feeding on algae.
Red pencil slate urchins are very sensitive to light. Being nocturnal allows them to conveniently move in the night without having to dodge behind rocks to avoid being hit by sunlight. In Hawaii, sea temperature is lower at night than day time by a few degrees, which makes it more comfortable for red pencil slate urchins to hunt as well as reproducing as studies have shown that sea urchins in general do not reproduce as much when the temperature is above 21°C.
Environmental pressure that may have resulted to this behaviour adaptation may be global warming. As we all know, global warming has been resulting in increasing sea temperatures which makes the environment even more uncomfortable for red pencil slate urchins to feed and reproduce. Also the fact that sea urchins are sensitive to light may have also caused it to adapt to night life for activity.
Structural Adaptation #1:
The mouth of most sea urchin species, red slate pencil urchin included, consist of 5 teeth and a tongue-like flap (refer to figure 5). The chewing devices of all sea urchins are commonly known as the Aristotle’s lantern. After studies and close examinations, it is confirmed why the teeth of sea urchins are so strong. It is because their teeth are made by calcite, a soft mineral made of calcium carbonate, and contain crystals of magnesium calcite which is much harder than pure calcite. Scientists have also discovered that the concentration of the calcite increases gradually as it gets to the tip of the tooth, which is used for grinding.
Despite the fact that the red slate pencil urchins already have very uninviting spines for defence, their teeth come in handy when they need to bore a hole out of a rock to make shelter for the day. As well as that, the teeth also come in handy when they are consuming kelp, mussels and barnacles, which are all part of their diet.
Environmental pressure that could have resulted in this structural adaptation would be the red slate pencil urchin’s need to shelter in coral reefs and rocky shores. The Aristotle’s lantern may have been slowly developed by the sea urchin’s constant grinding in the rocks in order to find shelter. Its need to devour kelps and barnacles may also have resulted to the development of the Aristotle’s lantern as they are now easier for sea urchins to consume.
Structural Adaptation #2:
All sea urchin species have spines, however pencil urchins have spines that are rather blunt than other species such as the purple sea urchin (refer to figure 6) and the black long-spined sea urchin which have the longest spines out of all the other sea urchin species. A red slate pencil urchin’s spine can be up to about an inch long and it can be regenerated when damaged or lost.
Some sea urchin species’ spines are sharp and hollow with poison fluid that can be used to attack predators; however the red slate pencil urchin’s spines are solid and blunt. This makes it less dangerous for predators to touch. Despite the lack of defence provided by its spines, the blunt spines of a red slate pencil urchin can be used to grip objects on the sea floor or bore holes out of rocks to make shelter. Although it has tube feet for used for travelling, the big blunt spines do help a red slate pencil urchin to get around quite efficiently. As mentioned before, the red slate pencil urchins take advantage of their blunt spines to fit into crevices conveniently.
Environmental pressure that could’ve resulted in this structural adaptation would be the fact that it occasionally needs to create shelter out of rocks in coral reefs. Also, having spines could fulfil its need to consume kelp as its tube feet and spines make it much easier to get a good grip of the kelp.
Physiological Adaptation
Sea urchins have a very amazing physiological adaptation and that is the light-sensitive molecules that are concentrated along the spines. According to scientists and marine biologists, this may mean that the spherical sea urchin may just be one big eye itself. With no organ dedicated for sight, the sea urchins can see visual details by screening out light from off angles. As this research continues, scientists begin to unravel the mystery of more complexities to sea urchins’ physiological structure.
With rather sparsely-packed spines being able to reflect light from off angles, it is true that the red slate pencil urchin may not have a sharp vision as sea urchins with densely-packed spines (eg: purple sea urchin), the light-sensitive molecules are still able to provide a relatively good vision for the red slate pencil urchin. With a relatively good vision, they can see when a predator is nearing and can spot comfortable places for shelter.
The environmental pressure that could have resulted in this physiological adaptation would be the sun. Over time the sun may have developed the sensitivity of the light-sensitive molecules, gradually improving the vision of the red slate pencil urchin.
Sea urchins, or urchins, are small animals with round and spiny ‘tests’ (shells) that inhabit most of the oceans in the world. The name urchin used to be a name for ‘hedgehog’ and since sea urchins inhabit the sea, they are known as the ‘sea urchins’. They belong to the phylum Echinodermata which means ‘spiny skin’ in Greek.
The Red Slate Pencil Urchin is mainly found in the tropical waters of the Indo-Pacific region, specifically in Hawaii. This type of urchin has blunt, solid spines that resemble pencils, hence the name ‘pencil urchin’. The name of the urchin also originated from the fact that its spines were once used as writing material on slate boards.
Scientific Classification
Level
Classification
Kingdom
Animalia
Phylum
Echinodermata
Class
Echinoidea
Order
Echinoida
Family
Echinometridae
Genus
Heterocentrotus
Species
H. mammillatus
Habitat
Geographical location
The Red Pencil Slate Urchin mainly resides in the Eastern Indo-Pacific Ocean that surrounds many volcanic islands including Hawaii. red pencil slate urchins are commonly found in the Hawaiian Islands (refer to figure 1). Hawaii has a very stable climate, although it may vary a bit, the temperatures are mostly the same throughout the year during winter and summer. The average temperature is 26.6°C while the ocean water temperature varies from a warm 22.7°C to 26.6°C. According to previous experiments and studies, when temperatures are higher than 21°C reproduction decreased which means that there is a slight possibility that there may be a future decrease in reproduction of the red pencil slate urchins.
Red pencil slate urchins share the same home in the Hawaiian ocean with the green sea turtle and the bottlenose dolphin, however both of these animals are not their predators.
Sunlight, storms and the effects of these aspects
Hawaii, being the absolute surfer’s paradise and number 1 holiday location, is known for its always sunny skies. On sunny days, the sun can be very intense which is not a good sign for Red Pencil Slate Urchins as, like other sea urchins; they are very sensitive to light. This explains why they normally like to hide in shallow tide pools as the coral reefs and rocks can not only let them hide from predators but also let them find shelter from the sun. Red Pencil Slate Urchins are nocturnal; they spend most of the day time hiding in between or behind rocks avoiding the sunlight (refer to figure 2) and dislodging itself to find food when night arrives.
In the past, tropical storms and hurricanes have also been responsible for wiping out a great amount of sea urchins. Living in Hawaii, an island that sits on the edge of a tropical zone, it is rather prone to occasional tropical storms which, as a result, cause large waves that can dislodge Red Pencil Slate Urchins. This can cause a decrease to their population as they can be washed away from their food source. Although hurricanes are rare in Hawaii, when it does occur it can achieve the same result, causing damage to the Red Pencil Slate Urchin population.
Food source and predators
Red Slate Pencil Urchins are herbivores; they mainly feed on kelp, seaweed and algae. They are known to be extremely abundant and can cause disturbance to the kelp-forest ecosystem. This is because they feed on the hold fasts of kelps (refer to figure 3) which causes it to detach from its anchor, disabling it from regrowth. This is where the predators of Red Slate Pencil Urchins save the kelp-forest ecosystem by feeding on sea urchins, maintaining the ecological balance and sustaining the luxuriance of kelp forests. Apart from sea grass, Red Slate Pencil Urchins also feed on dead fish, mussels and barnacles which explain how they find food at ease the coral reefs of Hawaii. However Red Slate Pencil Urchins attract many predators on the coral reefs as well and these daring predators include molluscs and fish like the spotted oceanic triggerfish which are also found mostly in coral reefs. The spotted oceanic triggerfish are exactly opposite to the Red Slate Pencil Urchins; they are active during the day while they sleep soundly in between rocks at night. They are able to feed on many sea urchins (including the Red Slate Pencil Urchin) despite their sharp spines, by flipping them over and going through the shell through the soft tissue surrounding the mouth of the sea urchin. Triggerfish are capable of flipping the sea urchin by shooting a strong jet of water while the sea urchin is relaxed (since it would be resting during day time when triggerfish are active).
[Figure 3: Video of sea urchin feeding on kelp]
AdaptationsBehavioural Adaptation #1:
Red pencil slate urchins like to use their blunt spines to fit themselves tightly into small cracks between rocks (refer to figure 4). Many tourists who go out to explore the coral reefs in Hawaii do comment on the red pencil slate urchins to “disappear and be completely out of sight during the day time and magically reappear in groups during the night”.
By doing this, the rocks offer them a very good camouflage from predators during the day time while they are resting as well as the intense sunlight that they are sensitive to. Another reason why red pencil slate urchins hide themselves in tight crevices is to prevent themselves from being washed away by big waves or currents.
Environmental pressure that might have resulted in this adaptation could be tourism. This is because many tourists who visit Hawaii like to explore the beautiful underwater world and this may cause disturbance to red pencil slate urchins, causing them to hide themselves from these unwanted visitors during day time. Also, occasional tropical storms in Hawaii may have resulted in the red pencil slate urchins “knowing” how to hide in crevices to prevent being washed away by the big waves of the aftermath.
Behavioural Adaptation #2:
Red pencil slate urchins, like other sea urchin species, are nocturnal. As previously mentioned, red pencil slate urchins spent most of their day resting in safe shelters between rocks and come out during the night to hunt. To be specific, when it is dawn, red pencil slate urchins search for a good shelter in shady crevices. During the day, they stay in their shelter and do not conduct much activity. At dusk, after 3PM, red pencil slate urchins will dislodge themselves from their shelters and start to find food. At night time, during midnight until 3AM, is the period when they’re at their most active state. Usually at this time, they would be feeding on algae.
Red pencil slate urchins are very sensitive to light. Being nocturnal allows them to conveniently move in the night without having to dodge behind rocks to avoid being hit by sunlight. In Hawaii, sea temperature is lower at night than day time by a few degrees, which makes it more comfortable for red pencil slate urchins to hunt as well as reproducing as studies have shown that sea urchins in general do not reproduce as much when the temperature is above 21°C.
Environmental pressure that may have resulted to this behaviour adaptation may be global warming. As we all know, global warming has been resulting in increasing sea temperatures which makes the environment even more uncomfortable for red pencil slate urchins to feed and reproduce. Also the fact that sea urchins are sensitive to light may have also caused it to adapt to night life for activity.
Structural Adaptation #1:
The mouth of most sea urchin species, red slate pencil urchin included, consist of 5 teeth and a tongue-like flap (refer to figure 5). The chewing devices of all sea urchins are commonly known as the Aristotle’s lantern. After studies and close examinations, it is confirmed why the teeth of sea urchins are so strong. It is because their teeth are made by calcite, a soft mineral made of calcium carbonate, and contain crystals of magnesium calcite which is much harder than pure calcite. Scientists have also discovered that the concentration of the calcite increases gradually as it gets to the tip of the tooth, which is used for grinding.
Despite the fact that the red slate pencil urchins already have very uninviting spines for defence, their teeth come in handy when they need to bore a hole out of a rock to make shelter for the day. As well as that, the teeth also come in handy when they are consuming kelp, mussels and barnacles, which are all part of their diet.
Environmental pressure that could have resulted in this structural adaptation would be the red slate pencil urchin’s need to shelter in coral reefs and rocky shores. The Aristotle’s lantern may have been slowly developed by the sea urchin’s constant grinding in the rocks in order to find shelter. Its need to devour kelps and barnacles may also have resulted to the development of the Aristotle’s lantern as they are now easier for sea urchins to consume.
Structural Adaptation #2:
All sea urchin species have spines, however pencil urchins have spines that are rather blunt than other species such as the purple sea urchin (refer to figure 6) and the black long-spined sea urchin which have the longest spines out of all the other sea urchin species. A red slate pencil urchin’s spine can be up to about an inch long and it can be regenerated when damaged or lost.
Some sea urchin species’ spines are sharp and hollow with poison fluid that can be used to attack predators; however the red slate pencil urchin’s spines are solid and blunt. This makes it less dangerous for predators to touch. Despite the lack of defence provided by its spines, the blunt spines of a red slate pencil urchin can be used to grip objects on the sea floor or bore holes out of rocks to make shelter. Although it has tube feet for used for travelling, the big blunt spines do help a red slate pencil urchin to get around quite efficiently. As mentioned before, the red slate pencil urchins take advantage of their blunt spines to fit into crevices conveniently.
Environmental pressure that could’ve resulted in this structural adaptation would be the fact that it occasionally needs to create shelter out of rocks in coral reefs. Also, having spines could fulfil its need to consume kelp as its tube feet and spines make it much easier to get a good grip of the kelp.
Physiological Adaptation
Sea urchins have a very amazing physiological adaptation and that is the light-sensitive molecules that are concentrated along the spines. According to scientists and marine biologists, this may mean that the spherical sea urchin may just be one big eye itself. With no organ dedicated for sight, the sea urchins can see visual details by screening out light from off angles. As this research continues, scientists begin to unravel the mystery of more complexities to sea urchins’ physiological structure.
With rather sparsely-packed spines being able to reflect light from off angles, it is true that the red slate pencil urchin may not have a sharp vision as sea urchins with densely-packed spines (eg: purple sea urchin), the light-sensitive molecules are still able to provide a relatively good vision for the red slate pencil urchin. With a relatively good vision, they can see when a predator is nearing and can spot comfortable places for shelter.
The environmental pressure that could have resulted in this physiological adaptation would be the sun. Over time the sun may have developed the sensitivity of the light-sensitive molecules, gradually improving the vision of the red slate pencil urchin.
Sea Urchin of the Past
Sea Urchin of the Present
Sea Urchin of the Future
BibliographyWikipedia. (2010). Sea Urchin. Retrieved 19th of July, 2010, from http://en.wikipedia.org/wiki/Sea_urchin#Digestion
HawaiianForest.Com. (2008). Ha’uke’uke ‘Ula’ula — Red Slate Pencil Urchins of Hawaii. Retrieved 19th of July, 2010, from http://hawaiianforest.com/haukeuke-ulaula-red-slate-pencil-urchins-of-hawaii
To-Hawaii.Com. (2010). Hawaii Climate. Retrieved 19th of July, 2010, from http://www.to-hawaii.com/climate.php
Aquatic Community. (2006). Spotted oceanic triggerfish – Canthidermis maculatus. Retrieved 20th of July, 2010, from http://www.aquaticcommunity.com/marinefish/spottedoceanictriggerfish.php
TreeHugger.com. (2010). Sea Urchin Body Acts as a Giant Eye. Retrieved 20th of July, 2010, from http://www.treehugger.com/files/2009/12/sea-urchin-body-acts-as-a-giant-eye.php